1. Field of the Invention
The field of the invention is reaction force type disk brakes principally used for a vehicle, and more particularly, improvements in disk brakes of the type comprising a brake disk, a first and a second friction pad which are opposed to opposite faces of the brake disk, a brake caliper provided with a first and a second clamping arm for clamping the friction pads, a hanger pin bridged between the clamping arms for hanging both the friction pads, an urging member provided on the first clamping arm to urge the first friction pad against the brake disk, a stationary bracket for supporting the brake caliper through a pair of slide pins arranged on both sides of the urging member in a circumferential direction of the brake disk so as to permit the caliper to slide along a rotational axis of the brake disk, a braking-torque supporting portion provided on the bracket for supporting the braking torque of the first friction pad, and another braking-torque supporting portion provided on the brake caliper for supporting the braking torque of the second friction pad, the brake caliper including a first block having the first clamping arm, and a second block having the second clamping arm and secured to the first block.
The reason for forming brake disk of the two blocks in the mentioned manner is for the purpose of providing a good workability in machining a slide portion for the urging member in the first block.
2. Description of the Prior Art
The present applicant has previously developed a disk brake of this type as described in Japanese Utility Model Application Laid-open No. 80833/89.
In this disk brake, each slide pin is disposed in closer proximity to the urging member than each connecting bolt which connects the first and second blocks.
When the brake caliper is constructed of an assembly type from the first and second blocks as mentioned above, in order to increase the connecting strength between both the blocks so that the two arms are not opened or spreaded during operation of the urging member, it is desirable that the bolts should be disposed in the vicinity of the urging member. On the other hand, in order to support the brake caliper on the bracket with a good stability, it is desirable that the distance between the slide pins should be as wide as possible.
In the above-described disk brake, however, the positional relationship between the connecting bolts and the slide pins is reverse to the above-described demands, and therefore, an improvement in this respect is desired.
Another known example of a disk brake of this type is described in Japanese Utility Model Application Laid-open No. 74583/78.
In this disk brake, the urging center of the urging member located on the first friction pad in the central position in the circumferential direction of the brake disk and the rotational center of the brake disk are set on a first phantom straight line. A pair of fixed points at which the bracket is fixed on the knuckle of the vehicle are set on a second phantom straight line which intersects the first phantom straight line at a location closer to the rotational center of the brake disk than the urging center on face side of the brake disk. In addition, the fixed points lie on the both sides of the first phantom straight line, respectively. A pair of slide pin supporting points of the bracket are at locations closer to the outer periphery of the brake disk than a third phantom straight line which extends parallel to the second phantom straight line and passes the urging center.
However, if the slide pin supporting points are located in the above manner, the distance between the slide pin supporting point and the fixed point becomes longer and hence, when the braking torque of the second friction pad is applied to the slide pin supporting points through the brake caliper and the slide pins, a relative large rotational moment is produced about the fixed points.
This is undesirable for providing an improvement in durability of the bracket.
In the above-described disk brake, slide pin supporting portions of the bracket are disposed within a pair of windows provided in the brake caliper, and the pair of slide pins mounted on the brake caliper are slidably fitted into cylindrical guides of the slide pin supporting portions.
In such a disk brake, however, when the brake caliper supports the braking torque of the second friction pad, the urging forces acting in opposite directions are applied to opposite ends of each of the slide pins around the fitted portion of the slide pin in the cylindrical guide. This causes a torsional force to be applied to the slide pin supporting portion, resulting in a possibility of causing a defective smoothness in the sliding movement of the brake caliper.
Moreover, the slide pin functions as a bolt for connecting the blocks and therefore, the slide pin may be loosened by repeated urging force due to the braking torque to bring about a reduction in strength of the connecting structure for the blocks. There is also another problem of a degraded handling property in that if each pin is removed from the bracket for maintenance and inspection, the brake caliper is disassembled.
Further, in such a disk brake, the portion for supporting the brake torque and the portion for supporting the slide pin are commonly provided in a single block portion which is projectingly mounted on the bracket.
In such a disk brake, the brake torque of the first friction pad is supported on the braking torque supporting portion during braking and for this reason, a somewhat deflection is produced in the braking torque supporting portion. Under such a situation, if the single block is commonly used, the deflection at the braking torque supporting portion is transmitted directly to the slide pin supporting portion, with the result that a twisting is produced between the slide pin and the slide pin supporting portion, leading to a possibility of causing a defective smoothness in sliding movement of the brake caliper.
The present applicant has previously developed a further structure for preventing the slip-out of the hanger pin in the disk brake, as described in Japanese Utility Model Publication No. 6997/87.
This slip-out preventing structure comprises an annular groove provided in an outer peripheral surface at one end of a hanger pin projecting from the outer side of the brake caliper, and a locking groove provided in a slip-out preventing plate and engaged with the annular groove, the slip-out preventing plate being secured to the brake caliper by a screw. In this case, the hanger pin is provided at the other end thereof with a stopper which engages an opening edge of a pin hole in the brake caliper.
With such a slip-out preventing structure, however, the slip-out of the hanger pin can be reliably prevented, but a problem arises that if a gap is produced between the stopper and the opening edge of the pin hole, for example, due to working error or the like, the hanger pin is loosened axially and radially to generate an abnormal noise.